Chapter 6: Transport in humans

Main components of blood

- plasma

- red blood cell

- white blood cell

- platelets

plasma

- contains mainly water and substances such as glucose, salts, proteins, amino acids, fats, vitamins, hormones and excretory products such as urea

- also contains red and white blood cells

transports:

> blood cells around the body

> nutrients from the small intestines to other parts of the body

> excretory products from organs where they are produced to excretory organs for removal

> hormones from endocrine glands to target glans

Red blood cells

Features

> circular, biconcave shape

> no nucleus

> contains a red pigment called haemoglobin

> are flexible

- main function is to transport oxygen from the lungs to the other parts of the body

What are the adaptions that help red blood cells

- they contain haemoglobin that can combine reversible with oxygen

> in the lungs where oxygen concentration is high, haemoglobin binds to oxygen to form oxyhaemoglobin

> in tissues where oxygen concentration is low, oxyhaemoglobin releases its oxygen to the tissue cells

- they have a biconcave shape to increase the surface area-to-volume ratio

> this increases the rate of absorption and release of oxygen

- they are flexible and can change into a bell-shaped structure

> so that they can flow easily through narrow blood capillaries

- they have no nucleus

> there is more space for haemoglobin to be stores

How does the body compensate for the lower concentration of oxygen at high altitudes

- lower concentration of oxygen in the air at high altitudes than at sea level

- oxygen concentration gradient between the air and the lungs is less steep

> diffusion of oxygen into the lungs is slower

> less oxygen is absorbed into the bloodstream

- to compensate for this, the body responds by producing more red blood cells with more haemoglobin

> this will ensure that sufficient oxygen will be available for aerobic respiration to provide enough energy to meet the body's daily activities

White blood cells

- phagocytes

> phagocytosis is the process by which a white blood cell engulfs and destroys foreign particles such as bacteria

- lymphocytes

Produce antibodies that

> recognise foreign particles

> destroy-disease causing organisms such as bacteria and viruses

> cause bacteria to clump together for easy ingestion by phagocytes

> neutralise the toxins produced by bacteria

White blood cells are irregular in shape, they each have a nucleus

Platelets

- fragments of cytoplasm

- they contain an enzyme that catalyses the conversion of fibrinogen to fibrin threads

> these threads form a network that entangles red blood cells to form a clot

> this prevents excessive blood loss and the entry of harmful organisms into the bloodstream

How does blood clot

- the clot seals the wound preventing excessive loss of blood

- the clot so prevents foreign particles from entering the bloodstream

Process

> platelets are involved in converting the soluble protein fibrinogen to insoluble threads of fibrin

- this process involves enzymes (thrombin)

> fibrin threads entangle blood cells and the whole mass forms a clot or a scab

> the clot seals the wound, preventing entry of microorganisms and excessive loss of blood

Organ transplant and tissue rejection

- organ transplanted must not be rejected by the recipient's immune system

- any organ from another person may be treated as a foreign body by the recipient's immune system

> the recipient's white blood cell may respond by producing antibodies to destroy the transplanted organ

- a foreign tissue may be recognised by the white blood cells

- the white blood cells respond by producing antibodies to destroy the foreign tissue

> this is known as tissue rejection

Blood groups

- surfaces of red blood cells contain special proteins called antigens

> these same antigens are found on all red blood cells

- blood plasma contains antibodies, which are produced by the white blood cells, and are always present in the blood

> these natural antibodies will not react with the antigens on blood cells, but may react with the antigens on the red blood cells of another person

> this causes clumping of the red blood cells/agglutination of red blood cells

The four different blood groups

Blood group A

- antigen A (on rbc)

- antibody b (in plasma)

Blood group B

- antigen B (in rbc)

- antibody a (in plasma)

Blood group AB

- antigens A and B (in rbc)

- no antibodies (in plasma)

Blood group O

- no antigens (in rbc)

- antibodies a and b (in plasma)

What happens when different blood groups are mixed

- antibody of recipients blood group reacts with antigens of donor's blood group

Blood group A

- clumps: AB and B

- doesn't clump: A and O

Blood group B

- clumps: A and AB

- doesn't clump: B and O

Blood group AB (universal acceptor)

Blood group O (universal donor)

- clumps with everyone else

> rbc of group O blood do to have antigens A and B

- when group O rbc are transfused into a person of blood group A, the recipient's antibodies will not agglutinate with the donor's rbc

Parts of the circulatory system -1

heart

- keeps blood circulating throughout the body

- when the heart relaxes, it fills up with blood

- when it contracts, the blood is squeezed out with great force

> the blood then circulates through the blood vessels, which direct the blood flow around the body

Arteries

- blood vessels that carry blood AWAY from the heart

- the large artery that leaves the left side of the heart is the aorta

> it branches to form smaller arteries

Arterioles

- the arteries branch to form tiny vessels called artertioles

- the arterioles divide and ultimately, their branches become very tine blood vessels called capillaries

Parts of the circulatory system -2

Blood capillaries

- capillaries are microscopic blood vessels that are found between the cells of almost every tissue

- they have walls made up of only a single layer of flattened cells

- the capillary walls are partially permeable

> they enable certain substances to diffuse quickly through them

- small arteries branch out to form capillaries

> the numerous branches provide a large surface area for the exchange of substances between the blood and the tissue cells

> when an arteriole branches into many capillaries, the total cross-sectional area of the blood vessels increases

> this lowers the blood pressure in the capillaries

> the flow of blood is slowed down, giving more time for the exchange of substances

Venules

- before the capillaries leave an organ or tissue, they unite to form small vessels called venues

Veins

- venules in turn join to form bigger veins

- veins carry blood back to the heart

Structure of arteries

- receive blood directly from the heart

- they need to be able to withstand the high pressure of the blood forced out of the heart

- blood that flows in the arteries is fast-moving

> arteries have walls that are thick, muscular and elastic

> the elastic layer is much thicker in the arteries nearest to the heart

Adaptations of the structure of arteries

- the thick muscular walls help to withstand the high blood pressure in the artery

- the elasticity enables the artery wall to stretch and recoil or spring back

> this helps to push the blood in spurts along the artery and also gives rise to the pulse

Contraction and relaxation of muscles in the arterial wall

- the contraction and relaxation of muscles in the arterial wall brings about constriction and dilation of the artery

> when an artery constricts, its lumen becomes narrower and less blood flows through it per unit time

> when an artery dilates, its lumen becomes wider and more blood flows through it per unit time

What type of blood does the artery carry

- arteries carry oxygenated blood (except for the pulmonary arteries which carry deoxygenated blood from the heart to the lungs)

- arteries branch to form arterioles

Veins

- veins transport blood towards the heart

- blood pressure in the veins is much lower than the blood pressure in the arteries

- blood flows more slowly and smoothly in the veins

> the walls of the veins need not be as thick and muscular as those of arteries of about the same size

- veins also contain less elastic tissue

> instead, most veins have internal valves along heir length to prevent back flow of blood

- veins carry deoxygenated blood (except for the pulmonary veins which carry oxygenated blood from the lungs to the heart)

- they are formed when venues join together

How are substances transferred between capillaries and tissue fluid

- tiny spaces between tissue cells contain a colourless liquid, the tissue fluid

> this fluid transports substances between the tissue cells and the blood capillaries

- dissolved food substances and oxygen diffuse from the blood in the blood capillaries into the tissue fluid

> they then move into the cells

- metabolic (or excretory) waste products diffuse from the cells into the tissue fluid

> they are then transferred through the blood capillary walls into the blood

> the blood transports these waste products to the excretory organs for removal

Left side of the heart

- from the heart, the pulmonary ARTERIES carry blood to the lungs

- oxygen enters the blood at the lungs

> oxygenated blood is returned to the heart by the pulmonary veins

- oxygenated blood leaves the left side of the heart and is distributed by arteries to all parts of the body (except the lungs)

- veins carry blood from all parts of the body back to the right side of the heart

Structure of the heart

- entire right side (right ventricle + right atrium) receives deoxygenated blood

- entire left side (left ventricle + left atrium) receives oxygenated blood

Atria

- two upper chambers, the right atrium and the left atrium

- the atria receives blood from the veins

- the atria have comparatively thin muscular walls

> since they only force blood into the ventricles that lies directly below them

> this does not require high pressure

Ventricles

- two larger lower chambers, the right ventricle and the left ventricle

- ventricles have comparatively thick muscular walls

> the left ventricle muscle is much thicker because it pumps blood around the whole body and this requires high pressure

> the right ventricle has thinner walls than the left ventricle since it only pumps blood to the lungs, which is close to the heart

Median septum

- this is a muscular wall that separates the right and left sides of the heart

> it runs down the middle of the heart

- the median septum prevents the mixing of deoxygenated blood in the right side with the oxygenated blood in the left side

- mixing of deoxygenated with oxygenated blood will reduce the amount of oxygen carried to the rest of the body

Valves in the heart

- Flow of oxygenated and deoxygenated blood through the heart is controlled by the closing and opening of valves found in the heart

Tricuspid valve

- prevents backflow of blood from the right ventricle to the right atrium

Bicuspid valve

- prevents backflow of blood from left ventricle to the let atrium

Aortic valve (semi-lunar valve in the aorta)

- prevents backflow of blood from aorta to the left ventricle

Pulmonary valve (semi-lunar valve in the pulmonary artery)

- prevents backflow of blood from pulmonary artery to the right ventricle

What paths does blood take through the heart - pt 1

1

- Deoxygenated blood from the body is returned to the right atrium by two large veins called the venae cavae

- upper venae cavae transport blood from the head, neck and arms to the heart

- lower venae Cavae transports blood from the rest of the body (excluding the lungs) back to the heart

2

- from the right atrium, blood passes through the tricuspid valve into the right ventricle

- tricuspid valve consist of three flaps that point downwards into the ventricle

- these flaps are attached to the walls of the right ventricle by cord-like tendons called chordae tendineae

3

- from the right ventricle, blood leaves the heart by the pulmonary arteries to the lungs

4

- pulmonary veins transport oxygenated blood from the lungs to the left atrium

What paths does blood take through the heart - pt 2

5

- blood passes from the left atrium through the bicuspid valve into the left ventricle

- the bicuspid valve has two flaps that point downwards into the left ventricle

- the chordae tendineae prevent the flaps from being reverted into the atrium when the right ventricular muscles contract

6

- from the left ventricle, the blood leaves the heart and enters the aorta to be distributed around the body through different arteries

- two small coronary arteries emerge from the aorta

> they bring oxygen and nutrients to the heart muscle

What happens when there is a hole in the heart

- the hole may present in the median septum separating the left and right atria or the left and right ventricles

- blood will flow through the hole, mostly from the left side of the heart to the right side

> this is because the pressure in the left side is higher than the right side

> this results in the mixing of oxygenated and deoxygenated blood, which causes less oxygen to be transported to the body cells for respiration

- people with this condition may suffer from shortness of breath, fatigue, and in serious cases, heart failure

Cardiac cycle

1

- atrial muscles contract, forcing blood into the ventricles

2

- after a short pause, the ventricular muscles contract, causing a rise in pressure in the ventricle

> the rise in pressure causes the bicuspid and tricuspid valves to close to prevent back flow of blood into the atria

- the semi lunar valve open

> blood flows from the right ventricle and left ventricle into the pulmonary artery and aorta respectively

3

- as the ventricular muscles contract, the atrial muscles relax

- right atrium receives blood from the venae cavae while the left atrium receives blood from the pulmonary veins

4

- the ventricular muscles then relax

> fall in pressure causes the semi-lunar valves to close to prevent back flow of blood from pulmonary artery and aorta into ventricles

- the bicuspid and tricuspid valves also open and blood flows from atria into ventricles

5

- atrial muscles contract again and the whole cycle repeats

What is systole and diastole

systole (contraction) and diastole (relaxation)

Pressure changes in the heart (tb page 119)

1

- slight increase in ventricular pressure is due to the contraction of left atrial muscles, forcing blood into the ventricle

2

- ventricular muscles begin to contract

- bicuspid valve closes

3

- ventricular muscles continue to contract without change in volume of blood

- pressure continues to rise

4

- pressure in ventricle becomes higher than that in aorta

> aortic valve (semi-lunar valve in aorta) opens

> volume of blood in ventricle decreases as blood is forced into the aorta

5

- ventricular muscles begin to relax

> drop in pressure causes aortic valve to close to prevent back flow of blood into ventricle

6

- ventricular muscles continue to relax without change in volume of blood

7

- bicuspid valve opens when pressure in ventricle becomes lower than that in atrium

8

- pressure in ventricle rises as blood continues to enter the ventricle from the atrium

2, 3, 4, 5 > ventricular systole

6, 7, 8 > ventricular diastole

Main arteries of the body

Arteries leaving the heart

- pulmonary arteries from the right ventricle

- aorta from the left ventricle

From the aorta, following arteries arise

- arteries to the head, neck and arms

- the hepatic artery to the liver

- artery to the stomach and intestines

- the renal arteries, one to each kidney

Main veins of the body

Blood is returned to the heart by the main veins

- pulmonary veins bring blood from the lungs to the left atrium of the heart

- upper vena cava returns blood from the head, neck, and arms to the right atrium

- lower vena cava brings blood from the rest of the body to the right atrium

Lower vena cava receives blood from various veins from the lower body

- the renal vein bringing blood from the kidneys

- the hepatic vein bringing blood from the liver

Hepatic portal vein

- veins from small intestine do not open directly into the lower vena cava

- instead, they unite to form the hepatic portal vein, which enters the liver and branches into numerous capillaries there

> hepatic portal vein arises from capillaries in the wall of the small intestines at one end and gives rise to capillaries in the liver at the other end

Coronary heart disease

- coronary arteries lie on the outside of the heart, branching from the aorta

> they carry blood to the muscles in the walls of the heart

- blood supply to the heart muscles can be greatly reduced due to blockage of the coronary arteries

> this can cause a heart attack

What happens during a heart attack

- blood flow to a particular part of the heart may be completely blocked

- due o the blocked blood flow, that part of the heart does not receive sufficient oxygen and nutrients

> that region of the heart muscle dies

- extensive heart muscle damage is often fatal as the heart is no longer able to pump blood to various parts of the body

Causes of coronary heart disease

- fatty substances and saturated fats may be deposited on the inner surface of the coronary arteries (atherosclerosis)

> this narrows the lumen of these arteries and increases blood pressure

- such an affected artery develops a rough inner surface

> this increases the risk of blood clot being formed in the artery

> if it occurs in the coronary arteries, the supply of blood and oxygen to the heart muscles may be completely cut pff

- oxygen is needed in aerobic respiration to release energy for the activities of the muscle cells

- without oxygen, the heart muscle cells may be damaged, and a heart attack occurs

Risk factors of heart disease

Smoking

- cigarette smoke contains carbon monoxide and nicotine which can increase the risk of coronary heart disease

- nicotine increase blood pressure and the risk of blood clotting in the arteries

- risk of smokers developing coronary heart disease is much higher than non-smokers

Unhealthy diet

- a diet high in cholesterol, saturated fats and salt content increases the risk of high blood pressure and heart attack

Genetic factors

- family history has a role in developing heart disease

- high blood pressure and cholesterol can run in the family

Age

- risk of heart attack increases its with

Sedentary lifestyle

- lack of exercise and being inactive lead to the build-up of fatty deposits that block the arteries

> regular physical exercise strengthens the heart and maintains the elasticity of the arterial walls

> risk of high blood pressure or hypertension can be greatly reduced